1. Field of the Invention
The present invention relates to ion etching systems, and more particularly to structure to reducing current density in a focussed ion beam deposition system.
2. Description of the Prior Art
In U.S. Pat. No. 4,607,333, entitled ELECTRON BEAM EXPOSURE APPARATUS, issued Aug. 19, 1986 to Yasutake et al, a method for compensating errors in magnetic deflection of an electron beam using an electrostatic deflector is described. No method of reducing current density is described nor is there any description of a grid structure.
In U.S. Pat. No. 4,416,724, entitled METHOD FOR PRODUCING INSULATOR SURFACES, issued Nov. 22, 1983 to Fisher, an ion beam is used to form an insulator. No method of modifying the current density is described. The use of a grid to measure the ion current is described, however, the grid is not used to modify the ion current in this patent. Also, the structure of the grid in the subject disclosure would be different in the use of a much finer grid.
In U.S. Pat. No. 3,622,741, entitled ELECTRON BEAM PROCESSING MACHINE HAVING MEANS FOR DEFLECTING IMPURITIES FROM THE PATH OF ELECTRON BEAM, issued Nov. 23, 1971 to Stelgerwald, a grid is part of an assembly which is used to ionize residual gas and deflect it from the path of the ion beam. No method of reducing the current density is described, and the grid structure and function is distinct from the present invention.
In U.S. Pat. No. 4,523,971, entitled PROGRAMMABLE ION PATTERNING SYSTEM, issued Jan. 18, 1985 to Cuomo et al, a grid with programmable applied voltages is used to produce a pattern on a substrate. The grid is used in a broad area ion source and is not suitable for use with a focussed beam system. This grid could not be used to reduce current density. The grid of the subject invention is a passive element with a fine structure while the grid in the patent is electrically active and is a coarser structure.
In U.S. Pat. No. 4,527,044, entitled APPARATUS FOR TREATING SAMPLE BY PULSED ELECTRON BEAM, issued Jul. 2, 1985 to Bruel et al, no method of reducing the current density is described. A grid is used as a simple, standard, extraction electrode. Again, this grid would not have the structure of the grid of the subject invention.
In U.S. Pat. No. 2,925,496, entitled APPARATUS FOR OBTAINING SUBSTANTIALLY UNIFORM IRRADIATION FROM A NON-UNIFORM SOURCE, issued Feb. 16, 1960 to Zovbek, an ion beam is passed through a shaped hole. By moving the sample, a uniform irradiation is produced from a non-uniform ion beam. No grid is employed and no method of reducing the current density is described.
In U.S. Pat. No. 3,440,466, entitled WINDOW SUPPORT AND HEAT SINK FOR ELECTRON DISCHARGE DEVICE, issued Apr. 22, 1969 to Calvin et al, a grid is used as a heat conductor. No method of reducing current is described.
In U.S. Pat. No. 4,450,031, entitled ION SHOWER APPARATUS, issued May 22, 1984 to Ono et al, a grid is used as a simple standard extractor in a plasma source. The grid is an active part of the source. The structure of the grid is not suitable for varying current density.
In U.S. Pat. No. 4,758,304, entitled METHOD AND APPARATUS FOR ION ETCHING AND DEPOSITION, issued Jul. 19, 1988 to McNeil et al, a grid is used in a simple plasma type ion source. The grids involved are electrically active parts of the ion source, not passive low transmission elements. The structure of the grid in this patent is too coarse for application with a focussed ion beam for varying current density.
U.S. Pat. No. 4,087,695, entitled METHOD FOR PRODUCING OPTICAL BAFFLING MATERIAL USING PULSED ELECTRON BEAMS, issued May 2, 1978 to Lee et al, has no method of modifying current density.
In U.S. Pat. No. 4,389,573, entitled PULSED ELECTRON BEAM DEVICE COMPRISING A CATHODE HAVING THROUGH HOLES, issued Jun. 21, 1983 to Iton, the use of grids to increase electron fluence is described. The grids are an active part of the source and are also too coarse.
In U.S. Pat. No. 4,457,803, entitled PROCESSING METHOD WITH FOCUSED ION BEAMS, issued Jul. 3, 1989, to Takigawa no grid or method of reducing current density is described.